First photometric and orbital period investigations of four W UMa-type eclipse binaries

Abstract

We presented the first photometric and orbital period investigations for four W Ursae Majoris-type binaries: V473 And, V805 And, LQ Com, and EG CVn. The photometric solutions suggested that V805 And and LQ Com are two total-eclipse contact binaries, while V473 And and EG CVn are partial-eclipse ones. V473 And and LQ Com belong to the A-subtype contact binaries, while V805 And and EG CVn belong to the W subtype. The O’Connell effects found in the light curves of V805 And, LQ Com, and EG CVn can be interpreted as a result of a cool spot on the surface of their less massive and hotter primary components. Based on two different methods, the absolute physical parameters were properly determined. Combining the eclipse timings derived from our observations and survey’s data with those collected from literature, we investigated their orbital period variations. The results show that the orbital periods of V473 And, V805 And, and EG CVn are undergoing a secular decrease/increase superposed a periodic variation, while LQ Com exhibits a possible cyclic period variation with a small amplitude. The secular period changes are caused mainly by the mass transfer between two components, while the cyclic period oscillations may be interpreted as the results of either the light-time effect due to the third body or the cyclic magnetic activity. Finally, we made a statistical investigation for nearly 200 contact binaries with reliable physical parameters. The statistical results suggested that the W-subtype systems are more evolved than the A-subtype ones. Furthermore, the evolutionary direction of A-subtype into W-subtype systems is also discussed. The opposite evolutionary direction seems to be unlikely because it requires an increase of the total mass, the orbital angular momentum, and the temperature differences between two components of a binary system.

A Study of Six Extreme Low Mass Ratio Contact Binary Systems

“…Colour calibrated estimates, although widely used, have been shown to be cumbersome. Recently in an analysis of four contact binaries Hu et al (2022) found temperature variations between B − V and J − K color calibrations in excess of 500 K for 2 stars and 250 and 150 K for the other two. Ma et al (2023) reported variation in excess of 400 K between spectra and space based survey color databases.…”

Period Investigation on Two W UMa Binaries HH UMa and V1175 Her

“…Long term changes of the orbital period in contact binary systems are very common phenomena. According to the investigations, the period of a contact binary is not constant in many cases (Qian 2001;Qian et al 2007;Xiao et al 2016;Yang et al 2022aYang et al , 2022bPanchal et al 2022;Gao et al 2022;Hu et al 2022;Xu et al 2022). However, there are also cases with unchanged periods, such as LQ Com (Hu et al 2022) and PZ UMa (Zhou & Soonthornthum 2019).…”

OO Leo: An Active Contact Binary with Possible Solar-like Differential Rotation

“…In addition, a workable evolutionary sequence, from formation to the final destinies, has become clear (Eggleton 2012). However, there still exists some controversial and elusive issues, such as the evolutionary connections between two subtypes of contact binaries (Lucy 1973;Yakut & Eggleton 2005;Gazeas & Niarchos 2006;Gazeas & Stepień 2008;Zhang et al 2020c;Hu et al 2022), the orbital-period cutoff (Rucinski 1992;Li et al 2019;Zhang & Qian 2020), the mass ratio lower limit (Rasio 1995;Li & Zhang 2006;Arbutina 2007Arbutina , 2009Jiang et al 2010;Wadhwa et al 2021), and the magnetic activity origins of the orbital period variation (Applegate 1992;Qian et al 2007;Pi et al 2017;Hu et al 2020). To address these problems, more such systems, especially individual samples with rare characteristics, should be further investigated in great detail.…”